1. Field of the Invention
The present invention relates to image information reading devices for use in a copying machine, facsimile equipment and the like which optically scans an original document placed on a document base and reads the image information of the document, and more specifically, to an improved image information reading device in which a scanner comprising a light source, an optical system and a photoelectric converter is made thin and small in size, and its assembling accuracy and its vertical adjustment are improved.
2. Description of the Prior Art
Recently, there has been developed a heat transfer colour copying machine which uses, for example, a plural-colour heat transfer ink ribbon as a colour ink donor. A conventional colour copying machine typically comprises a device for reading the image information of an original document (scanner section) and an image forming section for thermally transferring an image information read by the reading device onto a paper. More concretely, the information reading device optically scans the original document placed on the document base to thereby read the image information of the document as a light colour signal, and the image information thus read is sent to the image forming section. The image forming section receives the image information sent from the information reading device, converts it to colour information indicative of corresponding inks of the heat transfer ink ribbon, selects corresponding ink portions of the ribbon in accordance with the respective colour information, and thermally transfer ink of the selected ink portions, one colour by another, to a paper by means of a thermal head sequentially, thereby achieving colour copy.
In the information reading device used in such a colour copying machine, a scanner comprises a light source for emitting light toward an original document placed on a document base, an optical system including a beam condensing fiber lens for guiding a reflected light from the document, and a photoelectric converter for converting the reflected light guided by the optical system to an electric signal. The scanner is reciprocated parallel to the lower surface of the document base to thereby optically scan and read the information of the document. In this case, the scanner, which is movably supported on a guide shaft and a guide rail as guide members disposed mutually parallelly under the document base, is guided along the guide shaft and guide rail so as to move parallel to the lower surface of the document base.
In the conventional information reading device, however, the guide shaft and guide rail are fixedly mounted to a frame of the device and thus the vertical position or parallelism of the scanner with respect to the lower surface of the document base is determined by the manufacturing and assembling accuracies of the frame. The same explanation holds true for the focus position of the optical system. For such reasons, in the case of a colour copying machine with especially a high required resolution, it is impossible to obtain such satisfactory vertical position or parallelism only with the dimensional accuracy of the device at the time of assembling, and therefore troublesome adjustment is necessary after the frame has been assembled.
Further, in such a conventional device, since the beam condensing fiber lens is disposed in such a manner that the optical axis of the lens is substantially perpendicular to the surface of the document, the overall height of the scanner is high, for example, about 60 mm. Accordingly, if the printed circuit substrates are positioned under the scanner, the information reading device cannot be made thin, therefore, the substrates are disposed next to the fiber lens. However, the device usually requires three substrates, each having a height of 53 mm when vertically disposed for a signal amplifier circuit an A/D converter, etc. resulting in a thick device.
Furthermore, in this type of device, a unit mounted with the mirror and lens, a unit mounted with the photoelectric converter and a unit mounted with the light source are provided separately, so that the assembling accuracy between these units cannot be made high. In order to improve the assembling accuracy, it is considered to provide an adjusting mechanism. However, this requires the increased number of necessary parts, making it difficult to render the device small, thin and light in weight.